Tsunami Design Approaches for Resilient Ferry Terminals

The Washington State Ferries system serves as critical infrastructure for the traveling public throughout the Puget Sound region. Disruption to ferry service can have major impacts on the travelers and commuters. A natural hazard that can affect ferry terminals are tsunamis. Ferry terminals and pier structures are located overwater, typically a few feet above high tide, making them susceptible to tsunami velocities and inundation. Common perception is that tsunamis have a large impact on coastal regions from the Cascadia Subduction Zone, but Puget Sound is also vulnerable from not only the Cascadia fault, but also the Alaska and local faults. There are 20 Washington State ferry terminals in Puget Sound, each of them being susceptible to the effects of a tsunami. As an effort to make ferry terminals resilient to this hazard, probabilistic tsunami modeling at each ferry terminal was performed which includes all known seismogenic sources at different return periods. This modeling produced probabilistic tsunami amplitude, velocity, and momentum flux specific to each terminal site. The data was then converted to load cases using the most appropriate applications from ASCE 7-22 and AASHTO Guide Specifications for Bridges Subject to Tsunami Effects. Neither document has a design approach specific to pier structures, so interpretation is necessary for application. This study will describe the methodology of using the site-specific tsunami data to develop loading and design criteria on the ferry structures.